Aircraft Systems Chapter 6: Fuel Systems
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Questions and Answers

What is the primary function of the inhibitors added to jet fuel?

  • To control corrosion and bacterial growth (correct)
  • To enhance fuel pressure
  • To increase volatility for easier starting
  • To reduce the weight of the fuel

    • Which of the following is NOT a subsystem in jet transport fuel systems?

  • Storage
  • Vent
  • Filtering (correct)
  • Distribution

    • Why is low volatility desirable in turbine engine fuels?

  • To prevent vapor lock and evaporation in fuel tanks (correct)
  • To prevent fuel contamination from microbial growth
  • To allow for easier restarts at high altitudes
  • To improve fuel efficiency during flight

    • What is the purpose of surge tanks in jet transport fuel systems?

    <p>To manage fuel overflow and system venting</p> Signup and view all the answers

    What is a common characteristic of integral fuel tanks in jet transports?

    <p>They use structural space in the aircraft's wings</p> Signup and view all the answers

    Which factor is a conflict when choosing turbine engine fuel?

    <p>The demand for low volatility vs the need for high volatility</p> Signup and view all the answers

    What role does venting play in transport category fuel systems?

    <p>It connects tanks to vent space and prevents pressure buildup</p> Signup and view all the answers

    What is the primary purpose of check valves, also known as flapper valves, in fuel tanks of aircraft?

    <p>To prevent fuel from flowing outboard during maneuvers</p> Signup and view all the answers

    How does an ejector pump maintain fuel flow at the inlet of the engine driven pump?

    <p>By creating low pressure using a venturi as fuel circulates</p> Signup and view all the answers

    What is a key difference between fuel strainers and fuel filters in aircraft fuel systems?

    <p>Strainers primarily block large debris, while filters handle smaller contaminants.</p> Signup and view all the answers

    What is the likely consequence if an engine driven fuel pump experiences cavitation?

    <p>Reduced fuel flow causing engine performance issues</p> Signup and view all the answers

    What role do turbine engine fuel control units play in the fuel system?

    <p>They regulate the pressure and supply of fuel with precision.</p> Signup and view all the answers

    What is the primary function of baffle check valves in integral fuel tanks?

    <p>To ensure fuel boost pumps have fuel regardless of aircraft attitude</p> Signup and view all the answers

    What is the primary function of the fuel cooled oil cooler (FCOC) in the Boeing 727?

    <p>To both heat the fuel and cool the engine oil</p> Signup and view all the answers

    What safety procedure must be followed before performing maintenance on an integral fuel tank?

    <p>Empty the tank completely and purge fuel vapors</p> Signup and view all the answers

    How do manually-operated gate valves differ from motor-operated valves?

    <p>They can operate without electrical power in emergencies</p> Signup and view all the answers

    What role do fuel flow indicators play in jet transport aircraft?

    <p>They serve as the primary means for monitoring fuel delivery to the engines</p> Signup and view all the answers

    Where is the temperature sensor typically located in the fuel system of a jet transport aircraft?

    <p>In a main fuel tank</p> Signup and view all the answers

    What role does the electric motor play in motor-operated valves?

    <p>To either allow or stop fuel flow to various tanks</p> Signup and view all the answers

    Why are access panels important for integral fuel tanks?

    <p>They provide access for inspection and repairs of fuel systems</p> Signup and view all the answers

    Which of the following types of fuel tanks is NOT commonly found in aircraft?

    <p>Expandable fuel tanks</p> Signup and view all the answers

    What mechanism allows fuel flow to continue around a clogged filter?

    <p>Fuel filter bypass</p> Signup and view all the answers

    What is a significant precaution when entering an integral fuel tank?

    <p>Using respiratory equipment</p> Signup and view all the answers

    In what scenario is a manually-operated gate valve especially important?

    <p>As a backup during electrical failures</p> Signup and view all the answers

    What kind of warning light is triggered by low fuel pressure in jet transport aircraft?

    <p>Boost pump failure warning light</p> Signup and view all the answers

    Which of the following statements is true regarding the positioning of manually-operated gate valves?

    <p>They are installed in the fuel feed line to each engine</p> Signup and view all the answers

    What does the sump area in an aircraft fuel tank collect?

    <p>Contaminants and water</p> Signup and view all the answers

    Which system is often used for indicating fuel quantity in transport category aircraft?

    <p>Capacitance type fuel quantity indication system</p> Signup and view all the answers

    What is necessary for large aircraft maintenance personnel to do before entering a fuel tank?

    <p>Completely empty the tank and purge vapors</p> Signup and view all the answers

    What is a potential consequence of failing to purge fuel vapors before tank entry?

    <p>Increased risk of fire or explosion</p> Signup and view all the answers

    Which of the following components indicates various parameters on the fuel indicating system of jet transport aircraft?

    <p>Multifunction display (MFD)</p> Signup and view all the answers

    What is the primary function of boost pumps in aircraft fuel systems?

    <p>To provide fuel under positive pressure to the engine-driven pump</p> Signup and view all the answers

    What happens to fuel flow if both the boost pump and the engine-driven pump fail?

    <p>Fuel is supplied directly from the fuel tanks by gravity-feed</p> Signup and view all the answers

    How does a centrifugal boost pump operate?

    <p>It draws fuel from the center and expels it outward through an impeller</p> Signup and view all the answers

    What role does the outlet check valve serve in a centrifugal boost pump?

    <p>It prevents fuel from flowing back through the pump</p> Signup and view all the answers

    Which of the following describes the bypass valve in a fuel feed system?

    <p>It enables the engine-driven pump to pull fuel if the boost pump is not working</p> Signup and view all the answers

    What is the significance of maintaining positive pressure in a fuel system?

    <p>To prevent vapor lock under changing temperature and altitude</p> Signup and view all the answers

    What safety measure is taken in both types of centrifugal pumps to protect against contamination?

    <p>The inlet is covered with a screen to filter out foreign matter</p> Signup and view all the answers

    What design options are available for centrifugal boost pumps?

    <p>They can be submersed in the fuel tank or mounted outside with plumbing</p> Signup and view all the answers

    How does a centrifugal boost pump contribute to fuel transfer between tanks?

    <p>It draws fuel from one tank and pushes it to another using its impeller</p> Signup and view all the answers

    Which of the following is a critical reason for using centrifugal fuel pumps in aircraft?

    <p>To ensure consistent fuel delivery regardless of flight conditions</p> Signup and view all the answers

    Study Notes

    Aircraft Systems - Chapter 6: Fuel Systems

    • All aircraft require fuel to operate. Fuel systems consist of tanks, pumps, filters, valves, lines, metering devices, and monitoring tools.
    • Fuel systems must provide uninterrupted, contaminant-free fuel flow regardless of the aircraft's attitude.
    • Strong airframes are needed as fuel accounts for a significant portion of aircraft weight. Shifts in fuel load during maneuvers should not impact aircraft control.
    • Fuel flow must be at the proper rate and pressure for engine and auxiliary power unit (APU) function.
    • Fuel pumps should only draw from one tank at a time to prevent air from entering the system.
    • Turbine engine aircraft need systems for safely venting fuel, assuring independence between multiple storage/supply systems. Failure in one system shouldn't affect another.
    • Fuel storage systems for turbine engines need to withstand loads under typical operating conditions.
    • They must be isolated from personnel compartments and protected from hazards like unintended temperature changes.
    • Jet fuel systems must enable continuous operation for at least half an hour at maximum power or thrust. Systems must also allow for safe fuel jettisoning, when needed, for landing.

    Fuel Storage System

    • Turbine engine fuel must be able to withstand loads under typical operating conditions.
    • It must be isolated from personnel compartments to protect from unintended temperature influences.
    • Fuel systems need to provide at least half an hour of operation at maximum power or thrust and be capable of jettisoning fuel safely for landing.
    • Fuel being jettisoned must be clear of the airframe on transport category aircraft.

    Aircraft Fuel

    • Turbine engines use jet fuel (Jet A, Jet B), Unlike aviation gasoline.
    • Jet fuel includes various inhibitors to control corrosion, oxidation, ice formation, and microbial/bacterial growth.
    • Choosing the right jet fuel depends on factors like its volatility (to prevent vapor lock and evaporation). Turbine engines must start quickly and restart easily in cold environments. Fuels with higher volatility are beneficial in those situations.

    Jet Transport Aircraft Fuel Systems

    • Jet transport fuel systems have subsystems like storage, vents, distribution, feed systems, and indicators.
    • Integral fuel tanks are often used in the wings or fuselage.
    • Surge tanks, usually located in the wing, are used for fuel overflow. They drain fuel back into main tanks.
    • Surge tanks provide fuel system venting.
    • Transport category fuel systems must vent fuel through tubing and channels, connected to vent space in surge tanks. This is done regardless of aircraft attitude or fuel quantity onboard.
    • A transport category aircraft fuel distribution subsystem includes pressure fueling components, a transfer system, and defueling components including a fuel jettison system.
    • Single point pressure refueling using ramp refueling trucks allows filling of all fuel tanks with one connection, common at leading and trailing edge wing locations.

    Fuel Feed

    • Boost pumps move fuel to a manifold for transfer into tanks when the fuel valve is opened.
    • Transfer/crossfeed pumps & manifold can also supply engines if normal fuel feed malfunctions.
    • In-tank fuel boost pumps can be used for each engine's fuel at pressure.
    • Crossfeed valves connect tanks if boost pumps malfunction.
    • Some systems have a means for heating the fuel via heat from an engine.
    • This heat exchange with hot air / oil may also cool the engine oil.

    Fuel Indicating

    • Fuel indicating systems (fuel quantity indicators and other monitoring devices) display various parameters on the aircraft instrumental panel or multifunction display (MFD).
    • True fuel flow indicators are for monitoring fuel delivery to each engine.
    • Fuel temperature sensors in main fuel tanks detect temperature and trigger a warning if necessary.
    • Fuel filters have bypasses that allow flow around clogged filters.
    • Low fuel pressure warning lights alert pilots if necessary.
    • Digital fuel quantity gauges and totalizers provide information about the fuel load in each tank.

    Fuel System Components: Fuel Tanks

    • Fuel tanks come in three basic types: rigid removable, bladder, and integral.
    • Rigid tanks are strapped into/riveted/welded to aircraft structures; they often have baffles.
    • Bladder tanks are flexible; they include the features of rigid tanks. They are attached to the structure using clips or other devices.
    • Integral tanks are part of the aircraft structure, requiring baffling to prevent the fuel from sloshing, esp. during maneuvers. Each tank has a sump, a low-area section to catch any contaminants/water. Drain valves are used to remove contaminants from the sump.

    Fuel System Components: Fuel Valves

    • Fuel valves are used for controlling/directing fuel flow to desired locations/engines.
    • Manually-operated gate valves (ON/OFF) are used for fuel flow control & emergency shutoff.
    • Motor-operated valves utilize electric motors to control fuel flow.

    Fuel System Components: Fuel Pumps

    • Boost pumps supply fuel under pressure to the engine-driven pump, during engine startup or when the primary driven pump malfunctions.
    • Centrifugal pumps are central to fuel systems.
    • Outward flow of fuel from the impeller is prevented by check valves.
    • Bypass valves allow fuel to be transferred to the engine-driven pump if the boost pump is not operating.

    Fuel System Components: Ejector Pumps

    • Fuel tanks have areas dedicated to the boost pump installation with partitioned baffles and check valves, to direct the flow of fuel to the inboard/outboard area when needed.
    • Some aircraft utilize ejector pumps to keep a positive head of fuel at the inlet of the boost pump. An ejector pump has a venturi to draw fuel into the boost pump sump area of the fuel tank.

    Fuel System Components: Fuel Filters

    • All aircraft have fuel filters and strainers preventing foreign contaminants from reaching the engines.
    • Fuel strainers often use coarse wire mesh designed to catch large debris.
    • Fuel filters, usually fine mesh, are used to catch small, fine particulate matter or water, to protect the fuel control units, which are extremely sensitive. Bypass valves may be included in the filter assembly in case the filter is clogged to route fuel around the filter.

    Fuel System Components: Fuel Heaters

    • Fuel heaters maintain acceptable temperatures in fuel systems to prevent ice formation, especially crucial at high altitude.
    • Air/fuel heaters use warm compressor bleed air to heat the fuel.
    • Oil/fuel heaters use hot engine oil to heat the fuel.

    Fuel System Indicators

    • Fuel flowmeters use viscosity and mass to display fuel flow/consumption of the fuel flow.
    • Fuel temperature gauges monitor fuel temperatures detecting unusual changes that may cause ice formation.
    • Fuel quantity probes and compensators are installed in fuel tanks for indicating fuel level.
    • Drip sticks are used for approximate quantities of fluid in individual tanks.

    Fueling

    • Fueling methods include over-the-wing and pressure refueling.
    • Over-the-wing refueling involves a nozzle inserted inside the top of the tank when refilling is complete.
    • Pressure refueling involves a nozzle that locks into the fueling port and is used when tanks are full or if there is an emergency need to refuel. Monitoring gauges are used during pressure refueling to verify that the fuel storage is done correctly.
    • Safeties must be observed (no open flames, static buildup) when refuelling. This is done to prevent any potential fire hazards.

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    Related Documents

    Chapter 6 Fuel Systems PDF

    Description

    Explore the critical components of fuel systems in aircraft through this quiz based on Chapter 6. Understand the importance of uninterrupted fuel flow, tank management, and the structural requirements for safe aircraft operation. Test your knowledge on how fuel systems directly impact engine performance and safety.

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